This invention relates to powder spray systems, and, more particularly, to a self-contained, portable powder spray booth and powder recovery system.
The process of spraying products with a solid powder coating involves preparing the powder coating in finely ground powdered form and spraying it onto the parts in a manner similar to liquid paint. Conventionally, but not necessarily, an electrostatic charge is applied to the sprayed powder to enhance the attraction of the powder to the product. The electrostatic charge maintains the powder upon the product for a sufficient time period to permit the powder to be heated so that it melts, and when subsequently cooled, is firmly attached to the target substrate. Powder spraying techniques of the type described above are well known and widely practiced commercially.
In most applications, powder deposition is performed in a booth which provides a controlled area from which any oversprayed powder not deposited on the article is collected. Spray guns mounted in the booth and connected to a source of air-entrained powder, such as a powder feed hopper and powder pump, spray powder onto articles moving through the booth which are suspended from an overhead conveyor. Containment of the powder in the booth is aided by an exhaust system which creates a negative pressure within the booth and causes the oversprayed powder to be drawn through a filter system before the air is exhausted to atmosphere. Oversprayed powder is collected in a powder recovery system where it is either held or recirculated to the powder feed hopper.
In some prior art designs, the spray booth, powder recovery system and filter system are contained within a single unit mounted to the floor, as disclosed, closed, for example, in U.S. Pat. No. 4,409,009. The powder spray booth of this patent is formed with an opening through which articles to be coated are transported by an overhead conveyor. A blower located exteriorly of the unit creates a negative pressure in a powder collection chamber beneath the spray booth to draw oversprayed powder material from the booth and through filters located in the powder collection chamber. The filters remove the powder from the air before it is discharged to atmosphere, and the oversprayed powder remaining is collected in hoppers beneath the powder collection chamber and then transferred through feed lines to a source of powder material, such as a feed hopper, located remotely from the unit.
A more compact powder coating system is disclosed in U.S. Pat. Nos. 3,694,242 and 3,714,926 to Ofner wherein the source of powder material such as a container or vessel is located in close proximity to the spray booth mounted on a fixed frame. Oversprayed powder from the spray booth is returned through a suction line directly to the powder supply vessel where the recovered powder is thoroughly mixed with air and then fed to spray guns mounted in the booth. The powder supply vessel also contains a filter to remove powder from the air entering the vessel before it is discharged to the atmosphere. The compactness of the Ofner system is achieved by including the filter system within the powder supply hopper or vessel, and by recovering oversprayed powder directly from the spray booth rather than from a powder collection chamber and hoppers located beneath the spray booth.
Additional flexibility in certain powder spraying applications has been obtained in prior art systems which include a fixed powder spray booth, and a combined, filter system and powder recovery system which is portable. These systems are particularly useful in applications where frequent color changes are required. The powder spray booths of such systems are formed with an opening at the top or ceiling through which articles to be coated are transported along an overhead conveyor. A portable unit which is movable into position relative to the fixed booth includes a recovery system for collecting oversprayed powder from the booth and a filter system for filtering powder from the air discharged from the booth. The oversprayed powder collected by the recovery system is transmitted through feed lines to a powder feed hopper, or other source of powder material located exteriorly of the booth, which then returns the powder through separate lines to powder spray guns mounted to the booth. Examples of coating systems having fixed spray booths and portable filter-powder recovery units are shown, for example, in U.S. Pat. Nos. 4,498,913; 4,354,451; 4,245,551; 4,378,728; and 3,944,404.
A variation of the systems described above is found in U.S. Pat. Nos. 4,545,324, 4,354,451 and 4,506,625. In these patents, the coating system includes a spray booth with rollers which is movable along the floor with a portable filter-powder recovery unit for positioning at different locations in a building.
One limitation of the powder spray systems described above is the limited flexibility in accommodating different applications and/or different articles to be powder coated. The spray booths of each prior art system described above are one-piece units mounted to an integral filter-powder recovery system or adapted to receive a portable filter-powder recovery system. None of such powder booths can be readily modified to accommodate articles of widely varying shape and/or size without requiring modification of the filter-powder recovery systems with which they are used. This restricts the flexibility of any given system for use in different applications, and, as a result, a different powder coating systems must generally be designed for each individual application.